This invention relates to an ink jet wherein the ink employed within the jet is of the phase change type, which may be referred to as hot melt ink.
The phase change, or hot melt ink, of the type utilized in an ink jet is characteristically solid at room temperature. When heated, the ink will melt to a consistency so as to be jettable. A hot melt ink jet apparatus and method of operation are disclosed in copending application Ser. No. 610,627, filed May 16, 1984 now U.S. Pat. No. 4,390,369.
It has been found that improper heating may degrade the ink and thus the performance of an ink jet. In order to avoid such degradation by extended heating, copending application Ser. No. 661,029, filed Oct. 15, 1984, now U.S. Pat. No. 4,607,266, discloses a method and apparatus whereby the reservoir is allowed to cool during standby and only the head is heated, thereby limiting the amount of ink heated and minimizing degradation of the ink with its adverse affects on performance.
It has also been found that extremely high, localized temperatures in an ink jet apparatus can subject the localized ink to undesirable conditions which will result in localized ink degradation which, of course, can also affect performance. Moreover, temperature gradients, i.e., variations in temperatures from one location to another location, in the ink jet apparatus can adversely affect performance of the ink jet. In addition to degrading performance, the above-discussed temperature effects can adversely affect reliability.